Phosphorus fractionation chemistry across the Great Plains

The SGS-LTER research site was established in 1980 by researchers at Colorado State University as part of a network of long-term research sites within the US LTER Network, supported by the National Science Foundation. Scientists within the Natural Resource Ecology Lab, Department of Forest and Rangeland Stewardship, Department of Soil and Crop Sciences, and Biology Department at CSU, California State Fullerton, USDA Agricultural Research Service, University of Northern Colorado, and the University of Wyoming, among others, have contributed to our understanding of the structure and functions of the shortgrass steppe and other diverse ecosystems across the network while maintaining a common mission and sharing expertise, data and infrastructure.Includes bibliographical references.Phosphorus is one of the three important plant nutrients found in soils and has been used with great success as an index for soil and ecosystem development (Aguilar et al., 1988; Honeycutt et al., 1990; Vitousek et al., 2004). In general, phosphorus is has minimal solubility in soil because it participates in a number of secondary reactions after release from primary minerals as a result of weathering. Studies of the biogeochemical cycling of P in humid ecosystems has led to important insights about soil and ecosystem development. Arid and semi-arid ecosystems have largely been ignored under the assumption that chemical transformations are minimal. We conducted research on the biogeochemistry of P along a bioclimatic gradient in grassland ecosystems of the Great Plains. The overall goal of our research is to use a systematic approach to characterize and further quantify the P transformations in biogeographically diverse grassland ecosystems. Identifying P quantities originally contained in central Great Plains soil will allow us to assess 1) the relative importance of P in the biogeochemical behavior of grassland soils, 2) help us quantify the degree of chemical weathering in semi-arid-humid grassland ecosystems, and 3) elucidate cultural use and potential productivity of these ecosystems prior to use of commercial fertilizers. We sampled soils along a bioclimatic gradient that represent three grassland ecosystems, namely, the shortgrass steppe, the mixed-grass prairie, and the tallgrass prairie in eastern Kansas. The soils were collected from sites studied within the Long-Term Ecological Research Program in areas that had not been used for agricultural practices other than grazing. We conducted a sequential extraction procedure to identify the following P fractions: soluble, Al-bound, Fe-bound, occluded, and Ca-bound. Our results suggest that soluble P is generally below detection limits at these sites, illustrating the high turnover rate of available P in these undisturbed systems. The Al-bound fraction was variable across all sites. The Fe-bound P contributed to the total P fraction only from the mixed grass and tall grass prairies. The occluded P fraction was greatest in the shortgrass steppe, decreased dramatically as mean annual and primary production increase from west to east.NSF Grant No. 0217631

Chemical properties of 11 date cultivars and their corresponding fiber extracts

Date palm fruit from 11 Tunisian cultivars (Phoenix dactylifera L.) were analyzed for their main chemical composition. Results showed that date fruits were rich in sugar (79.93 - 88.02 g/100 g dry matter), fiber(8.09 - 20.25 g/100 g dry matter) and ash (1.73 - 2.59 g/100 g dry matter). Mineral fraction was dominated by potassium and sugar fraction was dominated by reducing sugar (glucose, fructose) except for Deglet Nour, Kentichi and Bajo which are rich in sucrose. Date fiber concentrates (DFC) were extracted and analyzed for their proximate content (moisture, fiber, protein, lipid and ash) and some functional properties such as water holding capacity (WHC) and oil holding capacity (OHC). DFC presented high dietary fiber content (90.71 - 93.92 g/100g dry matter). Protein and lipid contents (dry matter basis) ranged between 3.66 and 6.06 g/100 g and between 0.35 and 1.08 g/100 g, respectively. DFC presentedhigh WHC (6.20 g water/g dry fiber) and high OHC (1.80 g oil/g dry fiber). Results showed that dates could be a valuable source of highly techno-functional fibers that could be used in food formulations

Biologic Cycling of Silica across a Grassland Bioclimosequence

The dynamics of biologic Si cycling in grassland ecosystems are largely unknown and likely to impact mineral weathering rates regionally and diatom productivity globally; key regulatory processes in the global Si cycle are closely tied to the global carbon cycle. Across a bioclimatic sequence spanning major grassland ecosystems in the Great Plains, soil biogenic silica depth distributions are similar to that of soil organic carbon; however, unlike soil organic carbon, quantities of soil biogenic silica decrease with increasing precipitation, despite an increase in annual biogenic inputs through litterfall across the same gradient. Though comprising only 1–3% of the total Si pool, faster turnover of biogenic Si and annual cycling by grasses should positively impact mineral dissolution. Our results suggest that the largest reservoir of biogenic Si in terrestrial ecosystems resides in soils, and emphasize the potential significance of grasslands in the global biogeochemical cycle of Si

Wage led aggregate demand in the United Kingdom

The wage led aggregate demand hypothesis is examined for the United Kingdom over the period 1971 - 2007. Existing studies disagree on the aggregate demand regime for the UK, and this appears to be due to differing empirical approaches. Studies relying on equation-by-equation estimation procedures tend to find support for wage led aggregate demand in the UK, while the single study using systems estimation finds no support for the hypothesis. In order to resolve this incongruity, we test the wage led aggregate demand hypothesis in the UK using VAR models estimated on quarterly data. We use a liberal partial identification strategy based on movements in real earnings rather than in the labour share. The results provide support for the wage led aggregate demand hypothesis during the period of study

Ariel - Volume 2 Number 4

Copyright 1969 Arie

Clinical Implications of Referral Bias in the Diagnostic Performance of Exercise Testing for Coronary Artery Disease

BackgroundExercise testing with echocardiography or myocardial perfusion imaging is widely used to risk‐stratify patients with suspected coronary artery disease. However, reports of diagnostic performance rarely adjust for referral bias, and this practice may adversely influence patient care. Therefore, we evaluated the potential impact of referral bias on diagnostic effectiveness and clinical decision‐making.Methods and ResultsSearching PubMed and EMBASE (1990–2012), 2 investigators independently evaluated eligibility and abstracted data on study characteristics and referral patterns. Diagnostic performance reported in 4 previously published meta‐analyses of exercise echocardiography and myocardial perfusion imaging was adjusted using pooled referral rates and Bayesian methods. Twenty‐one studies reported referral patterns in 49 006 patients (mean age 60.7 years, 39.6% women, and 0.8% prior history of myocardial infarction). Catheterization referral rates after normal and abnormal exercise tests were 4.0% (95% CI, 2.9% to 5.0%) and 42.5% (36.2% to 48.9%), respectively, with odds ratio for referral after an abnormal test of 14.6 (10.7 to 19.9). After adjustment for referral, exercise echocardiography sensitivity fell from 84% (80% to 89%) to 34% (27% to 41%), and specificity rose from 77% (69% to 86%) to 99% (99% to 100%). Similarly, exercise myocardial perfusion imaging sensitivity fell from 85% (81% to 88%) to 38% (31% to 44%), and specificity rose from 69% (61% to 78%) to 99% (99% to 100%). Summary receiver operating curve analysis demonstrated only modest changes in overall discriminatory power but adjusting for referral increased positive‐predictive value and reduced negative‐predictive value.ConclusionsExercise echocardiography and myocardial perfusion imaging are considerably less sensitive and more specific for coronary artery disease after adjustment for referral. Given these findings, future work should assess the comparative ability of these and other tests to rule‐in versus rule‐out coronary artery disease